1. Field of the Disclosure
The invention relates to construction and can be used for the construction of industrial floors and rafts.
2. Description of the Related Art
Concrete floors are either made of plain or reinforced concrete. The amount of reinforcement, or lack thereof, is in general dictated by the anticipated loads and loading intensities, and it can also be stated that a thicker slab of plain concrete can perform as satisfactorily as a thinner reinforced concrete floor.
Another reason for reinforcing concrete is to control the cracking of concrete caused by restrained shrinkage, flexural moments, plastic settlement of the ground, and punching-out of point loadings.
In order to reduce the incidence of cracking and width of cracks, it is usual to divide concrete floors into adjacent smaller slabs so that a proportion of the shrinkage contraction movement can be concentrated and located in the joints rather than the formation of undesirable cracks. Joints are of various types such as sawn cuts at 5 m to 15 m distance apart in each direction, or full depth construction joints.
Joints in concrete floors are designed in the expectation that they will open over time. Shrinkage can cause joints to open significantly and curling may be observed at the edges of the slab if shrinkage is greater in the surface layers than underneath. The thinner the slab is, the quicker and earlier it will curl, causing crumbling of the joint edges, and increasing the likelihood of damage to equipment traversing the floor.
The reinforcing of concrete floors may consist of rebars of steel wire mesh placed in a single layer, two layers or even more, depending on the type of application.
The reinforcing of concrete floors may also be obtained by randomly mixing fibers into the concrete. The fibers may consist of steel wire or steel cuttings, or of synthetic fibers or sometimes both types of fibers together, and with or without meshes and rebars. The benefit of using fibers is in their capability to better control cracking, and in a simpler slab construction, as the need for placement of rebars or meshes can be eliminated in most cases.
The introduction of steel fibers into composite concrete can reduce cracking in industrial floors and foundation slabs. According to the literature, a steel fiber dosage rate of 40 kg per cubic meter of composite concrete can reduce free shrinkage by up to 15%.
Steel fibers, thanks to their ability to better control concrete cracking, have been used during the past 25 years only as reinforcing in joint-free concrete floors of slab size not exceeding 3500 m2 without joints, in accordance with best practice. However, neither shrinkage nor cracking is eliminated in these applications.
The closest prior art for the proposed invention is the composition of composite concrete for floor slabs as described in patent EP0137024. The known composite concrete contains cement, water, sand-stone mixture, naphthalene melamine sulfonate solution, and steel fibers with a diameter of 1 mm and a length of 60 mm. The ingredients content in 1 m3 of composite concrete comprises:
cement310 kg;water155 kg;sand-stone mixture with particle size to1550 kg; 16 mmsand-stone mixture with particle size390 kg;16-25 mmnaphthalene melamine sulfonate solutionapprox. 1.2% ofcement mass,steel fibers of diameter 1 mm and length 30 kg.of 60 mm
The design and construction of slabs placed using the prior art composite concrete composition is described in several technical standards from various countries, including, for example ACI 360 (USA), TR34 (UK), CUR36 (Holland), CUR 111 (Holland), ACI223 (USA), ACI544 (USA). However, it has been shown in practice that slabs using the prior art composite concrete composition possess the following deficiencies: limited size of composite concrete slab because of long-term cracking and curling of edges of the floor slab, joint opening, and relatively high consumption of cement because the slab must be placed to a thickness of at least 15 cm.